Assessing STI Syndrome Aetiologies

Assessing STI Syndrome Aetiologies

Determining the micro-organisms that cause genital discharge and genital ulcer disease is an important STI surveillance activity. This assessment of aetiologies of STI syndromes is especially important in countries where STI syndromic management and case reporting are usually performed. Knowing the organisms that account for the STI syndromes allows the STI control programmes to recommend effective treatment.

• 
  the syndrome of genital discharge (urethral discharge in men and vaginal/endocervical discharge in women, caused by gonorrhoea, chlamydia and others)
  
• 
  the syndrome of genital ulcer disease in men and women (syphilis, chancroid and HSV-2).
  

Syndrome aetiologies should be reassessed every two to three years, or more frequently if the need arises. For example, if there is a new outbreak of genital ulcer disease, your reassessment of which micro-organisms are causing disease would happen earlier.

The main purposes of assessing syndrome aetiologies are to:

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  provide data for guiding STI syndromic treatment
  
• 
  assist in the interpretation of syndromic case reports and the assessment of disease burden due to specific pathogens
  
• 
  design or modify guidelines for treating urethral discharge and genital ulcers.
  

requirements

A microbiologist experienced in STI diagnostic tests should develop laboratory protocols for determining which organisms are causing the symptoms. Laboratories should also have quality assurance and control protocols in place.
The range of diagnostic tests that may be used is broad. Many new tests are being developed. Selection of the test to use will depend upon local availability of resources.

Laboratory requirements, continued

Syndrome	Corresponding laboratory tests
Genital discharge	Microscopy (Gram stain of urethral discharge to identify Gram-negative diplococci bacteria, primarily N. gonorrhoeae) Gonorrhoea and chlamydia testing: culture for N. gonorrhoeae direct fluorescent antigen and enzyme-linked immunoassay (EIA) for C. trachomatis amplified (such as PCR or strand displacement amplification) and non-amplified nucleic-acid-based tests for both pathogens
Genital ulcer disease	Syphilis serologic testing (non-treponemal and treponemal) Dark field, direct fluorescent antibody test for syphilis Culture for H. ducreyi HSV-2 culture or antigen detection test Polymerase chain reaction (PCR) for T. pallidum, H. ducreyi and HSV-2 available in some settings

Discussing

the table

Looking at Table 6.6, answer the following questions:

1. 
   For which syndrome is it appropriate to perform microscopy?
   

2. 
   How would you test for syphilis in genital ulcer disease?
   

Testing

Selection of populations for assessing syndrome aetiologies depends on the number of cases available for examination at a single site. Syndrome aetiologies should ideally be assessed in:

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  different types of populations
  
• 
  populations with high rates of disease
  
• 
  populations with low rates of disease
  
• 
  different geographic locations.
  

If your country has limited resources, begin with an assessment of genital discharge and genital ulcer disease at a single specialised STI clinic. The clinic should:

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  have well-trained personnel who can perform high-quality Gram stain and microscopy
  
• 
  be able to perform syphilis serologic testing.
  

In many countries, reliable dark field microscopy is unavailable.

• 
  Syphilis serologic testing alone provides an incomplete assessment of genital ulcer aetiology. This is because many patients with chancroid and HSV-2 ulcers can have reactive syphilis serologic tests from previously treated or untreated (latent) infections.
  
• 
  A substantial proportion (10%-30%) of patients with primary syphilis will not yet have developed a serologic response to infection.
  

Sample size

The sample size depends on the specific aetiology and the expected prevalence of pathogens.
A minimum sample size of 50 or 100 specimens from consecutive patients with the specified syndrome (or other type of systematic sample) will provide adequate information for useful analyses.
Analysis

It is important to analyse STI data separately for each specific disease rather than reporting findings together. For example, cases of gonorrhoea should be analysed separately from cases of syphilis. The frequency of the various STI and risk behaviours should then be calculated and analysed by:

Analysis, continued

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  gender
  
• 
  age group
  
• 
  geographic area
  
• 
  marital status
  
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  other relevant characteristics.
  

These tests should be anonymous, so there is no way to give results to individual patients. But if for any reason these tests are conducted in such a way that the results could be linked back to the individual, patients need to be given results and treated.